Organic C Determination

ORGANIC C DETERMINATION Soil organic matter is all non-mineral fractions found as the constituent components of soil. This organic matter is usually a pile of leftover plants, animals and microorganisms, either that have undergone a partial or complete overhaul. In addition, materials that are more resistant to overhaul are then transformed by micro-bodies from the original material through rearrangement into brown or black and colloidal materials known as humus. Soil organic matter has an important role for the soil as a medium where plants grow. It is a regulator of humidity and aeration; structural stabilizers; nutrient sources for plants, especially N, P, S, and B; increasing the cation exchange capacity; and is a source of energy for microbody activities. Besides that, it plays a role as one of the characteristics in soil classification. The levels of organic matter in the layers of agricultural soil range from low up to percent in mineral soils and can reach 60% in organic soils. Under the processed layer, the organic matter content shows a downward trend. The content of organic matter can be estimated from the level of organic carbon. Generally, soil organic matter on average contains 58% C. The method of determining soil organic matter has been known for a long time and is widely known. Until now, the determination methods can be grouped into: (1) based on the loss of soil weight due to shaping, and (2) based on the level of element C. Aligned with the available time and facilities, in this practicum the second method will be carried out. Determination of soil organic matter content based on the amount of carbon Organic. The principle of this method is that easily oxidized organic carbon in the soil reduces the excess given Cr 2O7=. This reaction runs using energy generated from mixing two parts of concentrated H2SO4 with one part of K2Cr2O7 N. The remaining Cr2O7= can be known from the results of tetracyte withFeSO4 whose normality is known. Ophenantroloin-iron complex (ferroin) 0.025 M is used as an indicator of the titration endpoint. The reaction that takes place is basically as follows: 3 C + 2 Cr2O7= + 16 H+ H2O Cr2O7= + FeSO4 3 CO2 + 4 Cr3+ + 8 Cr2(SO4)3 + Fe3+ This method according to several researchers such as Schollenberger (1954) and Walkley (1947) was able to oxidize an average of 77% of all organic matter. 21 However, this method is also not free from several weaknesses such as interference that can be caused by the presence of Cl-, Fe2+, sulfides, and MnO2. However, to a certain extent, this disruption is still acceptable by using several conversion factors in the calculation of the final result. In this practicum, the determination of soil organic matter compiled by Walkley and Black (1934), which is commonly used in non-calcareous mineral soils from humid areas, will be tried. How Soil Organic Content Determination Works In this determination, the stages of work that must be carried out are: 1. Weigh 0.5 g of dry soil with 0.5 mm filtered air (1 g when organic matter content < 1%); Place in 500 ml Erlenmeyer. 2. With a pipette add 10 ml of K2Cr2O7 N while shaking Erlenmeyer slowly let the mixing take place with the soil. 3. Immediately add 20 ml H2SO4 concentrate by measuring in the smoke chamber while shaking quickly until well mixed. Try not to throw any soil particles into the upper erlenmeyer wall so that they are not evenly mixed. 4. Leave the mixture in the acid chamber for 30 minutes until it cools. 5. Dilute with 100 ml of ion-free water/distillate water. 6. Add 4 drops of 0.025 M ferroin indicator. 7. Immediately titrate with FeSO solution4 0.5 N until the solution remains burgundy. 8. The determination of blanks is carried out in the same way as above, but without using soil samples. (me K2Cr2O7 – me FeSO4) x f x 100 %C – organic = Bkm f = 1.33 me =NxV N = normality V = volume BKM = dry weight of the oven 105°C example of soil used. % organic matter = % C-organic x 1.724. 22